U.S. Pat. Nos. 4,929,495 and 5,021,529 teach carboxylated acrylate polymers for nonwoven fabric and formaldehyde-free self-curing interpolymers for paper and other nonwoven fabrics respectively. Crosslinlking of the latex binder may be brought about after latex drying to obtain the highest tensile properties. Crosslinking approaches employing methylol groups, either incorporated into the polymer binder, or through addition of a crosslinking agent, for example, melamine-formaldehyde resin, are commonly used. Methylol chemistry produces formaldehyde during curing, which can be objectionable. Further, relatively high temperatures (approximately 150° C.) are typically required to initiate the methylol crosslinking reactions. The high temperatures needed for some crosslinking reactions limit processing speeds, and add to energy costs in producing the bound paper or nonwoven.
Water dispersible polyisocyanates, such as disclosed in U.S. Pat. Nos. 5,252,696 and 5,563,207, from reacting polyisocyanates with monofunctional polyether alcohols containing ethylene oxide repeating units are known components in coating compositions where they can react with isocyanate reactive groups in aqueous coating compositions. Under proper reaction conditions, these materials can be dispersed in water without a significant amount of less desirable side reaction between the isocyanate group(s) and water occurring in the normal time period for use of the dispersed isocyanate containing mixture. In coating compositions, the inclusion of the water dispersible polyisocyanates results in higher crosslink density than in similar coating compositions without water-dispersible polyisocyanates.
Blocked polyisocyanates are used in water containing compositions to prevent the reaction of the isocyanate group(s) with water. Subsequent to water removal by evaporation, the blocked isocyanates can be unblocked, such as with heat, and regenerate the reactive isocyanate group that can then react with active Zerewitinoff hydrogen containing compounds. One such blocked polyisocyanate is described in U.S. Pat. No. 4,895,921.
U.S. Pat. No. 5,268,419 discloses a fast curing binder for cellulose comprising a solution copolymer of an olefinically unsaturated organic compound having at least one carboxylate groups, which is reacted with a primary or secondary amide of an olefinically unsaturated carboxylic acid. The product of said reaction is admixed with a non-formaldehyde containing latex carrier to produce a binder composition which reaches substantially fully cured wet strength in 8 seconds or less. U.S. Pat. No. 5,030,507 teaches emulsion binders which do not generate formaldehyde during cure. They utilize 2-20 parts meta or para-isopropenyl-α,α-dimethyl benzyl isocyanate. The products are heat resistant flexible products for use in roofing, flooring and filtering materials as well as facings and other applications in general purpose nonwoven products.